Preparing for the Worst: Stafford Dam Emergency Action Planning and Risk Awareness

2015 FMA Conference

Topics Project Overview Dam Breach

Scenarios Downstream Flooding Inundation Mapping Emergency Action

Plan Tabletop Exercise 3D Animation

Client:• North Marin

Water District• Novato, CA

(Marin County)

Subconsultant:• Jeffries Public

Safety Consulting• Dave Jeffries• Former City of Novato

Police Captain

Project Overview

Schedule (2015):• Project Kickoff – March• H&H Modeling – April• Inundation Mapping – May• EAP – May/June• Tabletop Exercise – June• After Action Report/Revised

EAP – July/August• 3D Animation – August

Project Overview Stafford Dam (Novato Creek Dam)

• Earthfill embankment• 650’ long at crest; 79’ high

above original ground surface• 4,430 ac-ft Storage Capacity • Built in 1951• 1985: Embankment enlarged,

raised 8’ and spillway reconfigured

• Dam/Spillway designed for PMF reservoir inflow of 12,305 cfs and PMF spillway outflow of 4,148 cfs

Stafford Lake provides 20% of the City of Novato’s Water Supply

Project goal was to identify risk and develop EAP in accordance with Federal and State standards

Dam Breach Scenarios (Hydrologic Analyses)

Overtopping failure ruled out because of spillway capacity and freeboard during the Probable Maximum Flood (PMF)

Piping failure during the PMF using BREACH

Maximum PMF Discharge is 4,150 cfs

Q100 = 2,000 cfs

Dam Breach Scenarios (Hydrologic Analyses)

Maximum Breach Outflow ~ 50,000 cfs

Downstream Flooding(Hydraulic Analyses)

2-dimensional hydraulic model (FLO-2D)

1-dimensional embedded channel

Reduction factors to account for volume in buildings and reduced conveyance due to buildings

Inundation Mapping

1973 Inundation Map

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Emergency Action Plan

Emergency Action Plan

EAP Purpose Reduce loss of life/Minimize property damage Assist NMWD in communicating emergency

levels• Provide guide for possible evacuation of at-risk

persons Provide dam technical info and remediation

actions• Conducting inspections after earthquake, placing

sandbags, riprap materials if spillway has eroded, plugging seepage areas with hay bales, bentonite, etc.

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EAP Key Components Responsibilities 5 Step Action

Process Evacuation Mitigation and

Remediation Actions

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EAP Key Components Emergency Notification

Flowcharts Quick Reaction Checklists

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Tabletop Exercise Conducted 3.5 hour tabletop exercise on

6/25/15 Examined awareness, notification, and response

to incident using Dam EAP Responses to 3 Scenarios:

1. Unusual, slowly developing event

2. Potential dam failure that is rapidly developing

3. Imminent dam failure

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Tabletop Exercise North Marin Water District Marin County

• Department of Public Works• Flood Control & Water Conservation District• Sheriff’s Office of Emergency Services• Fire Department

City of Novato• Department of Public Works• Police Department• Fire District

Novato Unified School District• San Marin High School

California Highway Patrol Consultants

• Jeffries Public Safety Consulting• Michael Baker International

Tabletop Exercise - Areas Examined How NMWD becomes aware of dam safety event How decisions are made/notifications are

completed Response issues involving multiple organizations Community notification and evacuation issues Response levels and associated notifications

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3D Animation Process Create and Run XPSWMM 2D Model

Refine Surface in 3rd Party Software

Import Data into

Animation Software

Isolate Scenes

“Hotspots”

3D Animation Process

Surface 3D Model• Civil3D• SketchUp• VR-Design Studio

For More Information

Michael Skowronek, GISP, CFM, AICPmskowronek@mbakerintl.com510-879-0958

Jeffrey Crumpjcrump@mbakerintl.com760-603-6265